This invention relates to alternating current solid state watthour meters of the electronic type and more specifically to current transformers used in such type watthour meters.
Consumers of electricity who are anxious to lower their utility bills may resort to various techniques. One possible approach is to vary the electrical characteristics of the load connected to the electric utility. If, for example, a diode is placed in series with the load, a direct current component is superimposed on the alternating current flowing through the load. A direct current component can also be introduced by using an internal source of direct current such as a battery.
Where an alternating current flowing in a current transformer has a direct current component superimposed of the alternating current, a DC magnetizing current in the core of the transformer can result, which DC magnetizing current tends to build and saturate the core. When saturation occurs the alternating current component in the primary winding of the current transformer no longer induces a signal in the secondary winding which is proportional to the input AC component. Where a current transformer, saturated in this manner, is part of an electronic or solid state watthour meter, the meter is rendered ineffective for accurately measuring the power being consumed by the load.
An object of the present invention is to provide a compensating means for counteracting any direct current saturation of a current transformer in an electronic watthour meter.
Another object of the present invention is to provide a compensating means that permits the current transformer in a watthour meter to operate in the linear region in the presence of a DC magnetization current.